it would be easier if some sort of documentation would be available, especially if you are new to docker.
I found that if an existing docker network is in use (like with RC (cause of the communication between Mongo / RC & Hubot)) you can use the docker network external (https://docs.docker.com/compose/networking/ @ the bottom of the page). after setting the network config i can give each docker compose component it owns static ip (within the rocketchat_default network range).